Septic Arthritis: A Case Study
By Joseph Brooks, DO, MHA
Abstract: Septic arthritis is a serious musculoskeletal condition that must be recognized and treated promptly. This case report highlights the need for physicians to entertain a broad differential for acute monoarthritis in the outpatient setting. There can be value in identifying common signs, symptoms, and pursuing diagnostic testing, however, an accurate diagnosis most often depends on the quality of the clinician’s history, physical exam, and index of suspicion. Current standard of care treatments are reviewed here. There remains a need for further research in this area and development of guidelines for the treatment of septic arthritis.
Presentation of Case
A 61-year-old man presented to his primary care physician with left hip and groin pain. The pain began three days prior as he stood from his recliner. He described the inciting event as non-traumatic, but resulting in a sudden onset of sharp, 6/10, non-radiating pain in the left groin. Weight bearing made it worse and relative rest made it better. The patient had been taking over-the-counter (OTC) ibuprofen as needed, with some relief. He denied any associated numbness, tingling, or weakness. He had no loss of bowel or bladder function and reported no history of hernias.
The patient described chronic low back pain and a dull ache in his left hip for several months, but the new pain was more severe and in a different location.
The patient’s medical history included chronic low back pain for 18 months, paroxysmal atrial fibrillation and trivial mitral valve regurgitation for the last three years, eustachian tube dysfunction with granulations of a post-mastoidectomy cavity, and a history of chronic lung disease secondary to tuberculosis, for which he was disabled. The patient was taking metoprolol succinate extended-release tablets 50mg daily, aspirin 325 mg daily, and ibuprofen OTC as needed for pain. The patient’s surgical history included a right myringotomy with tube placement, a simple left mastoidectomy with two debridements, and an appendectomy.
Upon physical exam in the office, temperature was 100.0°F, blood pressure 110/74 mmHg, pulse 92 beats per minute, respiratory rate 20 breaths per minute, height 67 inches, and weight 152 pounds. The heart had a regular rate and rhythm. The lungs were clear to auscultation. The patient’s left hip/groin pain was reproducible with standing, worse with external rotation and extension of the left hip, and relieved by flexion to 45°. Musculoskeletal exam revealed 5/5 muscle strength bilaterally and equal in the lower extremities and muscle stretch reflexes were 2/4 bilaterally and equal at the patella and Achilles. Sensation was intact to light touch and the patient had a negative straight leg raise and negative FABERE test. Osteopathic structural exam revealed a lumber somatic dysfunction, L2-L4 Neutral SRRL.
The initial assessments for this patient included Psoas syndrome, somatic dysfunction of the lumbar spine, and chronic low back pain.
Osteopathic manipulation to L2-L4 was performed using muscle energy and paraspinal inhibition with objective and subjective improvement in the patients low back. Counterstrain to the left iliopsoas was attempted without significant relief. The patient was given prescriptions for ibuprofen 800mg and cyclobenzaprine 5mg, each to be taken three times daily, with instructions to follow up in one week.
Two days later, the patient complained of fever and vomiting which developed overnight and worsening left hip pain. The pain was now 10/10 and constant in the left groin, thigh, and calf. The next day, the patient reported ongoing fever, chills, and night sweats. He was advised to return to the office for reexamination.
Upon repeat physical examination, temperature was 101.5°F (tympanic), blood pressure 110/62 mmHg, pulse 88 beats per minute, and respiratory rate 20 breaths per minute. The patient’s general appearance was uncomfortable and unwell, and he was unable to find a comfortable position in which to sit. The heart had a regular rate and rhythm. The lungs were clear to auscultation. The abdomen was soft, non-tender, with bowel sounds positive in all four quadrants. Musculoskeletal exam revealed an antalgic gait and tenderness to palpation medial to the left ASIS over the left inguinal ligament and medial thigh. Inspection and palpation of the femoral triangle were negative for a femoral hernia. Additionally, inspection and palpation of the ingume canal were negative for a direct or indirect inguinal hernia. Testicular exam was within normal limits, without evidence of torsion or epididymitis.
The patient was then admitted to the hospital. Initial work up included a complete blood count (CBC), complete metabolic profile (CMP), lactate dehydrogenase (LDH), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and a computed tomography (CT) scan of the abdomen and pelvis with oral and intravenous contrast, blood cultures from two sites, and urinalysis (UA).
The result of the CT scan was positive for a left acetabulofemoral joint effusion consistent with a septic joint (Figure 1 and 2). The CBC, CMP, LDH, and UA came back within normal limits, but the sedimentation rate and CRP both came back elevated (Table 1). Interestingly, the white blood cell count was within normal limits at 9,600.
On day two of the hospital stay, a fluoroscopically guided left joint aspiration was performed, removing 5ml of purulent appearing fluid (Figure 3). The cell count showed 29,370 white blood cells with 82 percent segmented neutrophil granulocytes and an additional 9 percent bands. Gram stain showed gram positive cocci (Table 2). Ceftriaxone 1gm IV and piperacillin/tazobactam 3.375gm IV were initiated empirically. Patient-controlled analgesia with morphine was initiated for pain control, and orthopedic surgery was consulted. The patient was then taken to the operating room for irrigation and debridement with arthrotomy of the left hip.
On day four of the hospital stay, blood cultures obtained upon admission, the joint aspiration culture, and the wound cultures all grew Methicillin-Sensitive Staphylococcus Aureus (MSSA).
Based on the sensitivities of the admission blood cultures, antibiotic therapy was changed to cefazolin 2g IV. The patient was discharged on day eight of the hospital stay, and continued on oral pain medications and IV antiobiotics for the next six weeks.
Discussion
Septic arthritis (SA) is a musculoskeletal emergency with a wide differential diagnosis (Table 3).1 Prompt identification and treatment of this condition is essential to avoid significant associated morbidity and mortality. SA has been shown to destroy cartilaginous joints in as little as one or two days, leading to irreversible functional impairment.2 SA has three main etiologic mechanisms: (1) hematogenous spread of bacteria, (2) migration of bacteria from a focus contiguous to a joint, and (3) direct inoculation of bacteria into the joint. Most cases of bacterial arthritis, as in this case, are the consequence of occult bacteremia.1,6,7
A recent prospective trial showed an annual incidence of culture proven SA of 1 in 62,500 adults. 3 Staphylococci or Streptococci were implicated in greater than 90 percent of the cases, and there was an 11 percent mortality rate despite appropriate antibiotic therapy.3 The most commonly affected joint is the knee, accounting for about 50 percent of cases, followed by the hip accounting for 15 percent of cases.3,4 The ankle (9 percent), elbow (8 percent), wrist (6 percent), shoulder (5 percent), and sternoclavicular joint can also be affected.
A recently published systematic review of the literature examined the value of history, physical exam and routine laboratory findings in the diagnosis of septic arthritis.5 The classic presentation of SA is an acutely swollen, painful joint with limited range of motion. However, differentiating SA of the hip from a sprain, strain, or spasm, as in this case, can be challenging, based solely on history and physical exam. In fact, the sensitivity of the non-specific symptoms and signs of joint pain, joint edema, fever, sweats and rigors are only 85 percent, 78 percent, 57 percent, 27 percent and 19 percent respectively.5 Equally as limited are the highly sensitive laboratory signs of abnormal peripheral WBC, ESR, and CRP. For example, ESR was found to be 95 percent sensitive, but only 29 percent specific for SA.5
When there is a clinical suspicion of joint infection, arthrocentesis and blood cultures should be obtained. Synovial fluid analysis should include culture, gram stain, leukocyte count with differential, and a wet prep for crystals.1,4,5,6 Clinical suspicion must be high in the face of common risk factors which may significantly increase the likelihood of septic joint. These include age greater than 80, diabetes mellitus, rheumatoid arthritis, recent joint surgery, skin infection, or skin infection plus joint prosthesis.4,5,6 Some of the most common differential diagnoses (Table 3) are also the most common concurrent diagnoses with septic arthritis. For this reason, it is recommended to test for conditions including crystal induced arthritis, rheumatoid arthritis, seronegative spondyloarthropathies, and Lyme disease.6
No guidelines currently exist for the diagnosis or treatment of SA.7 Standard of care for suspected SA includes both appropriate and immediate antibiotic treatment and adequate surgical drainage. Empiric antibiotic therapy should not be delayed for culture results. Gram stain should direct broad-spectrum coverage. If the initial gram stain of synovial fluid shows gram-positive cocci, as in this case, the drugs of choice are cefazolin (Ancef©) 1 to 2g IV every 8 hours for community acquired infection, and vancomycin 30mg/kg IV daily in two divided doses for hospital or nursing-home acquired infection. However, if the initial gram stain shows gram-negative bacilli, therapy should be initiated with a third generation cephalosporin, such as ceftazidime (Fortaz©) or ceftriaxone (Rocephin©) (2g IV every 24 hours).6,7
Given the lack of a definitive source of infection, other than occult bacteremia, and the scarcity of risk factors, the prognosis and risk of recurrence is difficult to estimate for our patient. One option for follow-up is to screen for concurrent diseases like rheumatoid arthritis and seronegative spondyloarthropathies that would put him at higher risk and possibly explain his illness.
Conclusion
Septic arthritis is a serious condition which requires a high index of suspicion to appropriately diagnose and treat. Definitive diagnosis requires arthrocentesis with appropriate work-up. Treatment guidelines are lacking, but the standard of care of empiric antibiotics and appropriate consultation should not be delayed.
Dr. Brooks is a 2007 graduate of A.T. Still University of Health Sciences-Kirksville College of Osteopathic Medicine, Kirksville, Missouri. He finished an AOA Traditional Rotating Internship at Trinity at Terrace Park in Bettendorf, Iowa in 2008. Dr. Brooks is currently a PGY-2 PM&R Resident at the University of Missouri in Columbia, Missouri.
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